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POWhat does ovly_debug_event do in chrome?
 

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  1. POWhat does ovly_debug_event do in chrome?
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    <p>I was looking at chrome's thread stacks when I noticed that a lot of threads have a trace similar to this:</p> <pre><code>0, wow64cpu.dll!TurboDispatchJumpAddressEnd+0x6c0 1, wow64cpu.dll!TurboDispatchJumpAddressEnd+0x4a8 2, wow64.dll!Wow64SystemServiceEx+0x1ce 3, wow64.dll!Wow64LdrpInitialize+0x429 4, ntdll.dll!RtlIsDosDeviceName_U+0x24c87 5, ntdll.dll!LdrInitializeThunk+0xe 6, ntdll.dll!ZwWaitForSingleObject+0x15 7, kernel32.dll!WaitForSingleObjectEx+0x43 8, kernel32.dll!WaitForSingleObject+0x12 9, chrome.dll!ovly_debug_event+0x16574 10, chrome.dll!ovly_debug_event+0x14904 11, chrome.dll!ovly_debug_event+0x14826 12, chrome.dll!ovly_debug_event+0x16d19 13, chrome.dll!ovly_debug_event+0x1bea1b 14, chrome.dll!ovly_debug_event+0xe8ff4 15, chrome.dll!ovly_debug_event+0x16b50 16, chrome.dll!ovly_debug_event+0x16ab2 17, kernel32.dll!BaseThreadInitThunk+0x12 18, ntdll.dll!RtlInitializeExceptionChain+0x63 19, ntdll.dll!RtlInitializeExceptionChain+0x36 </code></pre> <p>The chromium source has the following code in <code>sel_ldr.c</code> which seems to declare <code>ovly_debug_event</code> as an almost empty function:</p> <pre><code>void _ovly_debug_event (void) { #ifdef __GNUC__ /* * The asm volatile is here as instructed by the GCC docs. * It's not enough to declare a function noinline. * GCC will still look inside the function to see if it's worth calling. */ __asm__ volatile (""); #elif NACL_WINDOWS /* * Visual Studio inlines empty functions even with noinline attribute, * so we need a compile memory barrier to make this function not to be * inlined. Also, it guarantees that nacl_global_xlate_base initialization * is not reordered. This is important for gdb since it sets breakpoint on * this function and reads nacl_global_xlate_base value. */ _ReadWriteBarrier(); #endif } static void StopForDebuggerInit (uintptr_t mem_start) { /* Put xlate_base in a place where gdb can find it. */ nacl_global_xlate_base = mem_start; NaClSandboxMemoryStartForValgrind(mem_start); _ovly_debug_event(); } </code></pre> <p>This raises the question: Why does chrome seem to spend so much time in a function that is only for debugging and is almost empty in chromium?</p>
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